1. Field of the Invention
In general, the present invention relates to filter cartridges that are contained within the confines of a storm drain. More particularly, the present invention relates to the structure and composition of the filtering material used in such cartridges.
2. Description of the Prior Art
Many modern streets are designed and built with storm drains. The storm drains are periodically located along the curb of the street. The street is graded in such a manner so that any water falling onto the street will flow to one of the storm drains. This prevents water from collecting on the street and inhibiting the flow of traffic along the street.
Traditionally, curbside storm drains contain a catch basin that is connected to a below lying sewer with a large diameter pipe. The catch basin is commonly covered with a grate. The grate enables water to flow into the catch basin but prevents large objects, such as tree branches, from passing into the catch basin and blocking the sewer pipe. The catch basin itself collects debris that is heavier than water but is washed into the storm sewer by the force of flowing water. As a result, storm drains need periodic maintenance, wherein the debris collected in the catch basin is removed.
As water flows over a street to a storm sewer, the water often mixes with oil and other contaminants. The oil may come from automobiles that leak oil. Other petroleum based contaminants include grease, diesel fuel, hydraulic fluid and gasoline. The federal and state environmental protection laws set forth many guidelines governing the disposal of petroleum based contaminants. Generally, it is unlawful to dispose of petroleum based contaminants in the public sewer system or in any other flowing supply of water. As such, the rain runoff that passes into many curb side storm drains fails to meet the state and federal standards due to the petroleum based contaminants that wash into the storm drains with the rain water.
The prior art contains many different types of filter systems that are intended to at least partially purify the runoff water that passes into a storm drain. Certain prior art devices are filters that pass over the grate above the storm sewer. Such a filter is exemplified by U.S. Pat. No. 5,403,474 to Emery, entitled Curb Inlet Gravel Sediment Filter. In such prior art arrangements, the filter itself is accessible above the sewer""s grate. Consequently, the filter disrupts the levelness of a street""s surface and therefore is only good in certain temporary applications.
Since the catch basins of many storm drains are made of poured cement, it is not practical to change the structure of existing storm drains in order for those storm drains to accept filters. As a result, many filter configurations have been made that are adapted to be added to existing storm sewer designs. In a typical storm sewer, a ledge is formed around the rim of the catch basin. The drain grate rests upon the ledge, thereby covering the open top of the catch basin. The depth of the ledge typically corresponds to the thickness of the grate. As a result, the top of the grate lays in the same plane as does the surface of the street. In the prior art, there are filter structures that hang in the storm drain catch basin below the grate. Typically, such prior art filter structures engage the same ledge of the catch basin that supports the grate. As a result, a portion of the filter structure must be placed in between the grate and the ledge upon which the grate is designed to sit. Such prior art filter structures are exemplified by U.S. Pat. No. 5,223,154 to MacPherson, entitled System For Filtering Liquids In A Catch Basin Using Filters In Series And Overflow Channels; U.S. Pat. No. 5,372,714 to Logue, entitled Storm Sewer Catch Basin And Filter and U.S. Pat. No. 5,284,580 to Shyh, entitled Refuse Collecting Frame For Sewer. One of the problems associated with such prior art filter structures is that the presence of the filter structure under the grate prevents the grate from seating properly onto the ledge at the top of the catch basin. As a result, the grate is held above its normal height, which may cause the grate to protrude above street level. If the grate does extend above street level, the grate becomes a tripping hazard. Furthermore, the grate can be caught by street plows and car tires, wherein the grate can be damaged or accidentally moved out of place.
U.S. Pat. No. 5,849,198 to Sharpless, the same inventor as herein, discloses a new filter system for storm drains that eliminates the disadvantages of the prior art filter systems mentioned above. The Sharpless system uses a filter assembly that is suspended below the grate of a storm sewer. Within the filter assembly is a disposable oil absorbing filter. The present invention is an improved embodiment of the disposable oil absorbing filter, the composition of which is described and claimed below.
The present invention is a disposable filter cartridge for a storm drain and the filter system that uses the improved filter cartridge. The filter cartridge has a pillow structure, wherein a water permeable scrim bag surrounds loose oil absorbing fibers. The oil absorbing fibers are preferably fabricated from melt blown polypropylene. The filter cartridge is placed in a filter cage that directs water flow through the filter cartridge yet prevents debris from reaching the filter cartridge. The filter cage is suspended below the grate of the storm drain by suspension elements such as chains or rods. The top of each of the suspension elements terminate at an attachment element that engages the grate of the storm grate. As a result, the filter cage and filter cartridge are suspended directly from the storm drain grate. By suspending the filter cartridge directly from the grate of a storm drain, the filter cartridge is positioned directly in line with the flow of water entering the storm drain. Furthermore, by suspending the filter cartridge from the grate, the designed orientation of the grate is not disturbed and the grate remains at or below street level.